Unable to log in to frequently visited sites

I've bee using VIvaldi on my new WIndows 10 laptop for a couple of months. Everything has been working fine, until today. I got a notification that an update was pushed and I needed to restart (not sure if this was a Vivaldi Update or a Windows update). Not only did this update wipe out ALL my saved passwords (I had to re-login to every site I visit), there's at least one site that I cannot log into at all--I click "login" and nothing happens. It's not an issue with the site because it works fine in Chrome and Firefox. I really like Vivaldi but I'm not going to use multiple browsers just so I can access one site. Has anyone else had this issue?

@JoCaT33: Hmmmm - nothing like that here. Is there anything special we ought to know about your installation, your extensions, or any 3rd party security software (some of which, lately, seems to be interfering with Vivaldi installations that they left completely alone until a recent update...)?